Twenty-five years ago today, one of the worst oil spills in United States history took place in Prince William Sound on the Gulf of Alaska. The water filled with about 10.8 million gallons of toxic crude oil, resulting in dead otters, birds and other wildlife. The world wouldn't see the likes of such a spill again until the Deepwater Horizon spill in 2010.

While cleanup efforts have helped restore the sound to its former state, effects from the spill still linger. Wildlife populations have returned to the area, but scientists continue studying the long-term effects of the spill, wondering just how much longer it will take for the ecosystem to bounce back.

"The understanding that lingering oil could have chronic effects on wildlife populations was a new and important finding, and one that we did not anticipate at the time that we started the research," Dan Esler, wildlife biologist at the U.S. Geological Survey, told NPR.

Fishermen in the region are still haunted by the spill, as their livelihoods have suffered. "The shrimp are slowly, slowly coming back," Bernie Culbertson told the Associated Press. "The crab aren't back. The herring aren't back. The salmon are back in abundance."

Below, we've rounded up images — then and now — of Prince William Sound. The top photo in each series is from 25 years ago; the present-day reality is pictured below.

Tankers

The Russian skimmer Vayadaghubsky worked the waters of Nuka Bay for oil from the Exxon Valdez oil spill on April 23, 1989.

Image: Stapleton/Associated Press

In this photo taken on June 30, 2012, the Exxon Valdez is anchored some six nautical miles off the Bhavnagar coast near Alang ship-breaking yard in western Indian state of Gujarat, India.

Image: Uncredited/Associated Press

Wildlife

While wildlife populations have returned, scientists still wonder about the long-term effects the oil spill will continue to have on species.

Cordova fisherman Tim Tirrell puts a dead sea otter into his boat after finding the oily animal on the beach of Johnson Bay on the Prince William Sound, Alaska.

Image: John Gaps III/Associated Press

Sea lions on oil-covered rocks and in the waters of Latouche Island, Prince William Sound, Alaska, on June 9, 1989.

Image: John Gaps III/Associated Press

Research biologist Don Calkins watches one of his research subjects, a 5-year-old Steller sea lion named Woody, as he swims around his pen at the Alaska SeaLife Center in Seward, Alaska, on April 28, 1998.

Image: Al Grillo/Associated Press

The U.S. Geological Survey report released on Feb. 28, 2014, concludes sea otters in Alaska's Prince William Sound have recovered to levels seen before the Exxon Valdez oil spill nearly 25 years ago.

Image: Mark Thiessen/Associated Press

Fishing Industry

Fishermen are still waiting for their fishing stocks to return to normal, pre-oil spill levels.

In this photo taken Feb. 26, 2014, vessels sit in the small boat harbor in Valdez, Alaska.

Image: Mark Thiessen/Associated Press

Recovery Efforts

Scientists and researchers continue to return to the area to see if any further cleanup is necessary.

A worker makes his way across the polluted shore of Block Island, Alaska, on April 17, 1989, as efforts are underway to test techniques to clean up the oil spill of the tanker Exxon Valdez in Prince William Sound.

Image: John Gaps III/Associated Press

Fisherman-turned-beach cleaner Ted Boyce cruises one of the beaches marked as oil-impacted near Andreon Bay, on the southeast side of Shuyak Island in Alaska in an undated photo.

Image: Marion Stirrup/Associated Press

In this April 11, 1989 picture, thick crude oil which washed up on the cobblestone beach of Evans Island sticks to the boots and pants of a local fisherman in Prince William Sound, Alaska.

Image: John Gaps III/Associated Press

A plastic bottle is embedded in a mixture of oil, sand and gravel on the southeast side of Shuyak Island, located 55 miles north of the city of Kodiak, the northernmost island in the Kodiak Island archipelago.

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